1. Field of the Invention
This invention relates to an electronic component mounting base board and a method of producing the same, and more particularly to a structure for electrically connecting a grounding pattern to a heat-sink plate.
2. Description of Related Art
As an electronic component mounting base board, there has hitherto been known a base board in which a dented mounting portion 97 for mounting an electronic component 98 is formed in an insulating substrate 99 and a wiring pattern 93 and a grounding pattern 91 are disposed on an upper surface and a lower surface thereof as shown in FIG. 20.
The wiring pattern 93 is electrically connected to the electronic component 98 through a bonding wire 982. A ball-shaped solder 92 for joining an electronic component mounting base board 9 to another member is joined to the wiring pattern 93.
Furthermore, a heat-sink plate 96 is bonded to the lower surface of the insulating substrate 99 through a conductive adhesion member 95 consisting essentially of silver as shown in FIG. 22. The grounding pattern 91 disposed on the lower surface of the insulating substrate 99 is broadly formed so as to surround a circumference of the mounting portion 97 as shown in FIG. 21.
As shown in FIG. 20, the grounding pattern 91 is electrically connected to the heat-sink plate 96 through the above conductive adhesion member 95.
The wiring pattern 93 and the grounding pattern 91 disposed on the upper and lower surfaces of the insulating substrate 99 are electrically connected to each other through an annular circuit 971 arranged on an inner wall of the dented mounting portion 97. Therefore, a current flowed into the grounding pattern 91 is transferred to the heat-sink plate 96 through the conductive adhesion member 95.
Moreover, a through-hole 991 may be formed instead of the annular circuit to provide electrical continuity between the wiring pattern 93 and the grounding pattern 91.
In the conventional electronic component mounting base board, however, the conductive adhesion member 95 consists essentially of silver, so that the cost becomes high. Further, the adhesion area is restricted, so that the scattering of resistance value in the conductive adhesion member 95 becomes large. Moreover, the heat-sink plate 96 is adhered to the metal face of the grounding pattern 91 through the adhesion member 95, so that the adhesion strength is weak.
In the production of such an electronic component mounting base board, as shown in FIG. 23, end faces of the insulating substrate 99 and the heat-sink plate 96 are contacted onto a positioning guide 960 to position the insulating substrate 99 and the heat-sink plate 96 and then the adhesion member 95 is cured.
When the thickness of the heat-sink plate 96 is as very thin as 0.1-1.0 mm, however, it is difficult to contact the end face 969 of the heat-sink plate 96 onto the positioning guide 960 and hence the positioning may not be conducted. Further, when the heat-sink plate 96 is adhered through the adhesion member 95 to the insulating substrate 99, the adhesion member 95 is overflowed between the plate 96 and the substrate 99 to adhere to the positioning guide 960 and there is caused a fear of complicating the positioning operation.
As shown in FIG. 20, the electronic component 98 may directly be connected to the heat-sink plate 96 located in the bottom of the mounting portion 97 through a bonding wire 981 to ground the electronic component 98. However, the bottom of the mounting portion 97 is narrow and is dented, so that the joining operation of the bonding wire 981 becomes complicated.